A cloth clamp set in an automatic sewing machine is normally required to vary the speed at which the cloth clamp travels so that a stitch needle is able to make a halt stitch (or stop stitch) and a condensed stitch at the start and end of a travel, as well as stitch with an acceptable sewing speed in a normal manner. Further, movement of the cloth clamp with a high speed is desired while the stitch needle is idle or out of stitch service.
Conventional devices proposed in connection with the above art have been designed including extremely complex electro-mechanical elements having especially designed solenoid-operated valves which are necessary to control oil flow through a number of by-pass lines. Therefore, individual parts of such devices had to be of high grade. The finished mechanism then became, as a whole, so intricate that such conventional devices are only employed in the manufacture of highly priced gentleman's suits. But, because of the high grade parts, employment of such conventional devices has been difficult in tailoring lower priced fabric products, for instance, working uniforms. This difficulty has prevented the popularizing of such an automatic sewing machine in the tailoring business.